This invention relates to a hook bar assembly for a multiple needle tufting machine, and more particularly to a clamp assembly for a tufting machine hook bar.
The conventional hook bars for multiple-needle tufting machines are long bars extending transversely of the machine below the needles and the base fabric. A conventional cut-pile hook bar has deeply elongated slots formed through its bottom face and uniformly spaced for receiving the hooks which cooperate with the needles to form loops in the yarns carried by the needles. For a narrow gauge, multiple-needle tufting machine, the looper slots in the hook bar must be formed close together. The closeness of the spacing of the looper slots is limited by the thinness of the walls between the slots. Conventional loopers or hooks are held in their respective slots by individual set screws which are threaded into each slot and engage the opposed walls or lands of the slots. Thus, the thinness of the walls is further limited by the diameters of the set screws. Moreover, the threaded movement of the set screws tends to expand and warp the slot walls or lands.
The prior U.S. Pat. No. 4,448,137 of Kenneth C. Curtis, et al, for "MODULAR HOOK BAR WITH GAUGE INSERT FOR TUFTING MACHINE" discloses a hook bar having a recess opening and within which is inserted an elongated transverse gauge bar or gauge member having transversely spaced hook slots for receiving the respective tufting hooks. Each of the shank portions of the corresponding hooks is clamped in the gauge bar by means of an upwardly directed set screw. One set screw is provided for each hook. Each set screw is directed upwardly and rearwardly at an angle to the bottom edge of the hook shank to bite into the force upwardly and rearwardly the shank of the tufting hook. In the Curtis hook bar, the gauge may be narrowed by staggering the set screws. Nevertheless, the gauge of the hooks, and therefore the gauge of the needles, is limited by spacing of the set screws and the set screw holes.
In some instances in which the above Curtis hook bar is made of soft material, there has been a tendency of the front-opening recess, receiving the gauge bar and the hooks, to open up because of the pressure exerted by the set screws against the individual hooks, forcing the hooks and the gauge bar upwardly against the upper surface of the recess. Even with the slightest opening of the recess, that is the spreading or separation of the top and bottom surfaces of the recess, the shanks of the hooks become loose within the recess. The loose hooks then become disaligned, lose their gauge, and interfere with the operation of their corresponding knives and needles. Moreover, the more the set screws are tightened, the looser the hooks become.
Another difficulty resulting from the utilization of a set screw with each individual hook, is that if each set screw is not exactly centered relative to its corresponding hook, the upward force of the set screw tends to push the hook to one side against the adjacent land of the gauge bar. The adjacent land bends to push against the hook on the opposite side of the land, which in turn pushes the next adjacent hook to produce a domino effect and a cumulative loosening and disalignment of the hooks with respect to the needles and knives.
Furthermore, where a set screw is employed for clamping each individual looper hook, the finer the gauge, the thinner the material separating the set screw holes, with consequent weakening and bending or even fracturing of the material between the set screw holes, both in the hook bar and in the gauge inserts or gauge bars.
As disclosed in the Curtis et al U.S. Pat. No. 4,448,137, the ends of hook bar sections or modules are lapped or offset to eliminate the problem of thin set screw walls at the ends of the hook bar sections. Such overlapped hook bar sections increase the difficulty of removing a hook bar section from the center of a machine because of the inter-locking or overlapping ends of the hook bar sections. Accordingly, with such overlapping hook bar sections, more time is required to replace or remove hook bar sections in the middle of the tufting machine.
Another type of hook bar or looper apparatus for mounting a plurality of looper hooks close together in order to provide a more narrow gauge for multiple-needle tufting machines, is disclosed in U.S. Pat. No. 4,217,837 of Max M. Beasley, et al, issued Aug. 19, 1980, for FINE GAUGE LOOPER APPARATUS FOR IN-LINE TUFTING MACHINE. In this looper apparatus, the hook slots are formed in an insert bar received in the front face of the hook bar, and the looper hooks are held in position by a plurality of clamp members threadedly secured to the hook block and against the front body portions of the looper hooks. The hook bars are made in the form of elongated modules which are mounted end-to-end, and each of the clamp members is adapted to secure a limited number of hooks upon the hook bar module.
In U.S. Pat. No. 4,445,446, of Max M. Beasley for KNIFE HOLDER MODULE FOR CUT PILE TUFTING MACHINE, clamp members in the form of cylindrical inserts are utilized to hold pairs of knives within the knife block members. Since the filing date of U.S. Pat. No. 4,445,446, the common assignee Tuftco Corporation, has substituted clamp balls for the cylindrical inserts to secure the pairs of knives within the knife block members with relative success. However, it was not obvious to use clamp balls to secure pairs of loop hooks because loop hooks are subject to different stresses and forces than are the tufting knives. Moreover, the hooks and knives serve different functions in the tufting process, i.e., seizing the yarn loop and cutting the yarn loop, respectively. Furthermore, the hooks and knives occupy different positions and attitudes. The hook shanks are substantially horizontal, while the knives are substantially vertical and are disposed at compound tension and pitch angles relative to the hooks.